Flow Mechanisms and Optimization Design Within a Super-Aggressive Intermediate Turbine Diffuser

Fully understanding of the flow mechanism of a super-aggressive intermediate turbine diffusers (AITDs) is the key to developing novel design techniques. Firstly, the flow analysis method of the AITDs was investigated in this study, and a new method for comprehensively evaluating the aerodynamic performance of the AITDs was proposed. Then, the typical flow characteristics in the AITDs were analyzed. Finally, it was further discussed that the integrated design method of the AITDs taking the combined impact of upstream and downstream into consideration. Results show that the calculation of diffusional efficiency considering the influence factors such as compressibility, area ratio and outlet face selection can more reasonably describe the diffusivity of the transition section. In the AITDs, the casing flow separation and the radial flow around the struts are stronger, resulting in the formation of a complex secondary flow structure, and flow loss in the AITDs is increased, which is a typical flow characteristic in the AITDs. By optimizing the local curvature of the casing and the hub, the thickness distribution and flow area, the efficiency of cascades increased by 4%, diffuser efficiency increased by 10.8% and second kinetic energy (SKE) decreased by 38%.